1. Field of the Invention
The invention is directed to a network which is constructed of optical and electro-optical, optically reciprocal elements, and can be coupled to a component which feeds an optical wave into the network, and has locations for effecting anisotropic reflections and has an arrangement of elements which isolates the optical source from anisotropic reflections from the network, particularly, a network formed as an optical homodyne or heterodyne receiver circuit.
2. Description of the Prior Art
It is known in the field of optical communications technology to isolate an optical transmitter from reflections. Such reflections particularly arise at the in-coupling location of a laser into a monomode fiber or into a monomode wave guide. Such reflection locations are essentially polarization-independent and are isotropic in this sense.
As known, for example, a polarization filter and a quarter wave plate which is provided with a perfect anti-reflection layer and--as seen in the direction of the approaching wave--is arranged behind the polarization filter are utilized for isolation from isotropic reflections. A polarized wave approaching the isotropic reflection location departs from the filter linearly polarized in the polarization direction prescribed by the filter, enters into the quarter wave plate linearly polarized and departs from the quarter wave plate circularly polarized. It hits the isotropic reflection location in this manner and returns circularly polarized and orthogonally relative to the approaching wave and, in the course of its further path in the direction opposite the approaching wave, is linearly polarized in the quarter wave plate and is polarized orthogonally relative to the approaching wave at the quarter wave plate. The filter can thus fully control the returning wave, so that the component which transmits the optical wave is protected against such reflections.
This known isolation principle is based on the resulting polarization transformation which is similar to that of a half wave plate and can, when using Jones matrices (CF., in this regard, Journ. of Optical Society of America 31 (1941), pages 488 through 493), be expressed by the equation ##EQU1## in which M.sub.Q is the Jones matrix of the quarter wave plate arranged at an angle of 45.degree. relative to the polarization direction of the emitted wave, M.sup.T.sub.Q is the matrix transpose of the the matrix M.sub.Q, I is the unit matrix, r is the reflection coefficient, g is a complex exponent, and M.sub.H is the Jones matrix of the half wave plate arranged at the angle of 45.degree. relative to the polarization direction of the emitted wave to obtain: ##EQU2## where j denotes the imaginary unit.
For example, an incident horizontally polarized, planar wave is transformed by equation (1) into a reflected wave which is vertically polarized and, which is orthogonally polarized relative to the incident wave.